Road log for Highway 638
NOTE: This road log was made prior to the construction on the Highway 17 bypass of the Garden River Reserve. For that reason I have not included that section of the Trans Canada Highway.
0 km = 0 mi. The Husky Service Station on Highway 17 near the eastern limits of the City of Sault Ste. Marie. Continue east through the Garden River Reserve to Echo Bay. Drive carefully while watching for pedestrians.
17.8 km =11.1 mi. Junction of Highway 638 and Highway 17 in the Town of Echo Bay.
Reset odometer. Continue along Highway 638.
5.4 km = 3.4 mi. Outcrops of pink-weathering sandstone of the Lorrain Formation.
10.6 km = 6.6 mi. Large rock-cuts on both sides of highway.
Click here to see a table of Formations of the Huronian Supergroup.
The west limit of the outcrop area is at N46deg,28.078min - W83deg,57.204min === NAD 83 (WGS 84) 17-273278E, 5015292N.
The sandstones, siltstone and minor mudstone exposed in the rock cuts are either the lower units of the Gordon Lake Formation or the uppermost rocks of the underlying Lorrain Formation of the Huronian Supergroup (Frarey, 1977). This is an interesting section of rock that reveal some events of the distant past.
A few small, ground-level rock exposures can be found on the north side of the highway a few tens of meters west of the high rock-cut. Mr. Ken Hatfield, formerly of Lake superior State University, brought these features to my attention many years ago. These low, rock exposures reveal evidence of ancient mud-cracks as polygonal patterns of apple-green mudstone outlined by pink sandstone (see photo 638-1).
NOTE: When I last visited this area the features described here were barely visible. It is hoped that future geology students will clear away the overgrown areas to reveal the ancient mud cracks. A dash of bleach may also help.
STOP 638-2
close observation near the western end of the long, high rock-cut will reveal that small-scale (about 20 cm high) cross-bedding is well-developed in pale-grey and pink sandstone.
A close examination of the rock exposure (and Photo of stop_638_2) will show that the bedding planes in the face of the outcrop are generally curving and intersect.
click here for more infoSections of the outcrop are composed of pale-grey sandstone in contrast to the pink sandstone that forms most of the exposure. It is significant that in places the boundary between the pink and pale-grey sandstone cuts across the stratification of the pink sandstone. This relationship shows that the bleaching occurred following the deposition of the pink sandstone. The bleaching may be the result of the removal of the reddish-coloured ferric iron in the pink sandstone or the reduction of the ferric iron to the less strongly coloured ferrous iron, resulting in the pale-grey coloured sandstone.
Additional evidence regarding the origin of the pale grey sandstone is revealed further east along the rock-cut.
In the central part of the outcrop thin beds of yellowish-brown mudstone and siltstone can be seen within the pink sandstone(see photo). Ripple-marks are visible in places.
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A mafic dike about 10 cm wide intrudes the sandstone near the fracture zone at N46deg, 28.045 min; W83deg. 57.088min. The dike has a strike direction and dip similar to that of the hematite-filled (reddened) fractures. This suggests that hot magma was in the vicinity when the fractures existed and thus may have provided the thermal energy to drive the fluids through the fracture system.
Stop 638-3
Near the east end of the rock-cut the pale-grey sandstone is cut by zone of dark red hematite staining (ferric iron) coloration along sets of steeply dipping, northeast striking fractures in the sandstone (see photo of Stop_638_3). A wide zone of pale-grey sandstone is found on both sides of the oxidized fractures (see photo Stop_638_3).
The writer provides a scenario to account for the observations in this rock exposure.(1) Rising Nipissing basaltic magma produced stretching and fracturing in overlying pink sandstone. The narrow mafic dike in the outcrop and the many Nipissing gabbro intrusions show that such magmas existed.
(2)Along these fractures, reducing fluids, emanating from the basaltic magma, passing upward reduced the ferric iron in the pink feldspar (or in the cement of the sandstone) thereby producing the bleaching of the sandstone over a broad area on both sides the fracture.
(3)The fluids transported the ferric iron into he fracture system became oxidizing with the precipitation of the much less soluble ferric iron as hematite within the fracture zone as a result of an encounter with oxygenated surface water
or- less likely
Oxygenated groundwater percolating downward from the Earth's surface may have deposited hematite in and near the fracture zone.
Stop 638-4
10.9 km = 6.7 mi. East end of outcrop at 17-273416E, 5150243N.
Before continuing beyond this point geology students should consider and discuss a possible environment of deposition for the rocks seen in the exposure they have just passed.23.2 km = 14.4 mi. Village of Leeburn.
25.0 km = 15.3 mi. East side of road.
Dark grey-green mudstone and siltstone of the Gowganda Formation. Thin-bedded to very thick bedded with some thin beds of pink siltstone.
25.3 km = 15.8 mi. Dark grey siltstone with smooth, striated outcrop surface due to most recent (Pleistocene) glaciation.
26.4 km = 16.4 mi. Nipissing granophyre and diabase, fractured and cut by calcite and iron carbonate veinlets.
30.7 km = 19.1 mi. Stop Sign at the village of Ophir.
32.7 km = 19.7 mi. West side of highway.
Matrix-supported conglomerate consist of pebbles and bounders dispersed in a fine matrix so that the pebble and boulder sized clasts are supported by the matrix, not in contact with each other. Such conglomerates are seldom. if at all, formed by the transport and deposition of clay to boulder-sized clasts by water or wind. Matrix supported conglomerates usually imply deposition from mudflows from melting glaciers or directly from ice as glacial till.
32.9 km = 20.4 mi. N46deg 26.674min;83deg 43.977min - West side of Highway.
A few granitic pebbles lie within dark grey laminated siltstone. Geologists generally agree that the only process that can allow the juxtaposition of pebbles or boulder-sized clasts in stratified, fine-grained sediment is the release of stones by melting icebergs onto the sea bed or lake bottom. Such "dropstones" provide the best evidence of a cold climate with the presence of floating ice (ice bergs) during the Middle Proterozoic Eon when the rocks of the Huronian Supergroup were deposited.
33.6 km = 20.9 mi.
Large gravel pit with high rock face on east side of the highway. A short unsurfaced road leads down to the gravel pit.
As the Pleistocene ice sheets melted the high rock face on the north side of the gravel pit is worn smooth by rushing water charged with abrasive sand etc. Vertical channels in the rock face suggest the erosive effect of sand-charged water under the extreme pressure of the adjacent ice sheet.
The northern section of the outcrop is matrix-supported conglomerate of the Gowganda Formation. A diabase dike (probably of Nipissing age) intrudes the southern part of the outcrop. The dike is about 10 meters wide (estimated).
36.2 km = 22.5 miles Rock Lake Road.
Stop 638.639.8 km = 24.7 mi. N46deg 23.506min;W83deg. 442w.182min.
Outcrops of pale-grey quartzite and jasper-quartz pebble conglomerate are found at east side of the highway. It is believed that the jasper pebbles were derived from Archean banded, iron-formation, which is well represented in Archean greenstone belt in the Batchewana area about 80 km north of Highway 556.
The distinctive, jasper-pebble conglomerate member of the Lorrain Formation (Frarey, 1977)is a minor but persistent unit. It has been found near the middle of the Lorrain Formation from the Sault Ste Marie area in the west to the Quebec border in the east. Although the high concentration of red, maroon and pink jasper presents a striking appearance it has a limited commercial use as a decorative stone because of its extreme hardness.
42.8 km =26.6 Outcrops of Lorrain Formation sandstone on west side of highway.
At least two faults show hematization in the fracture zone. A pebble unit is seen to be displaced along one of the fault.44.1 km = 27.4 mi. Bridge at Rydal Bank.
52.7 km = 32.7 mi Junction of Highway 628 and Highway 17 at Bruce Mines.
End of road log for Highway 638.
Gerald Bennett,Midland, 2017.